Excavating – Ditcher – Having endless digger
Reexamination Certificate
2000-08-04
2002-10-29
Pezzuto, Robert E. (Department: 3671)
Excavating
Ditcher
Having endless digger
Reexamination Certificate
active
06470607
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to methods and apparatus for constructing underground walls in trenches in the ground, such as soil-cement or slurry cutoff walls (COWs) and, more particularly, to the construction and operation of excavators for forming (excavating, digging) the trenches in the ground.
BACKGROUND OF THE INVENTION
Cutoff walls (COWs) are underground, preferably continuous and typically vertical walls, and may serve both as a foundation (or bearing) wall supporting an overlying structure, such as a pedestrian bridge, and as a diaphragm (or barrier) wall limiting seepage of fluids, such as ground water. Various techniques are known for constructing such underground walls. Very generally, a trench having a generally rectangular section is formed (excavated, dug) in the ground and is filled with cement or a hardening liquid such as cement slurry mixed with excavated earth and sand in the excavated trench to form a soil-cement wall. An exemplary resulting COW wall is also generally rectangular in section, and may have a wide range of dimensions including, but not limited to 100 meters long, 25 meters deep and 1 meter wide (thick).
In a one prior art technique for constructing underground walls, the trench is formed as a number of overlapping, parallel, cylindrical holes which are drilled vertically into the ground—for example, approximately 1 meter diameter holes spaced approximately 0.75 meters center-to-center and extending 25 meters into the ground. Apparatus for drilling and in-situ mixing to construct soil-cement piles (or columns) for soil solidification purposes is well known and shown, for example, in commonly-owned U.S. Pat. No. 5,411,353. Underground walls constructed according to this technique are generally not considered to be “continuous”, and are merely cited herein as contextual prior art.
In a prior art technique for constructing underground continuous walls, an excavator comprises an endless chain cutter (also known as a “trenching body”), resembling a chain saw bar and chain, comprising alternating cutter bits and agitator (mixing) bars arranged on an elongate guide post which extends into the ground. The guide post and endless chain are generally similar, but typically larger, than the endless chain and bar of trenchers for burying pipes, cables and the like, such as from Bobcat (TM) (e.g., the T136 hydrostatic trencher) and Ditch Witch (tm) (e.g., 1620, 3500). In this technique, the guide post is penetrated vertically into the ground, typically in a hole which has first been dug or drilled into the ground to the desired depth of the resulting wall, and the apparatus is then advanced (moved) slowly in a line along the surface of the ground. The excavated earth (and sand) is mixed with a hardening liquid such as cement slurry, and is injected into the trench behind the endless chain cutter. Examples of this technique may be found in Japanese Patent Publication No. 5-280043 (Document No. 4-79849) and in Japanese Patent Publication No. 5-280043 (Document No. 4-79850). As described in Document No. 4-79850 (at page 4 thereof):
“[An] underground continuous wall construction method . . . comprises the steps of digging a hole in the ground to a predetermined depth by means of a drilling device, inserting the endless chain cutter of the excavator into the hole, and excavating the ground in a predetermined direction by means of the endless chain cutter and removing the excavated earth and sand, while inserting an injection pipe behind the endless chain cutter to jet a hardening liquid mixed with the removed earth and sand into the excavated hole, thereby filling the excavated hole with any one of soil cement and soil mortar.”
FIGS. 1A
,
1
B, and
1
C illustrate an excavator
100
of the prior art, which is comparable to the excavator described in the aforementioned Document No. 4-79850. The excavator
100
is for forming a trench
102
in the ground
104
for constructing an underground wall.
FIG. 1D
illustrates an underground (cutoff) wall
160
being constructed in the trench
102
.
A starter hole
108
is dug or drilled vertically into the ground
104
, typically to the desired resulting depth D to the bottom
106
of the trench
102
being excavated, typically by means of a boring device such as an earth drill (not shown). An endless chain cutter
110
extends vertically into the hole
108
. The endless chain cutter
110
comprises an elongate guide post
112
(or “cutter post”), sprockets
114
and
116
at opposite ends of the guide post
112
, an endless chain
120
extending around the guide post
112
and the sprockets
114
and
116
, and a number of cutter bits
122
and agitator bars
124
alternately arranged on the endless chain
120
. It should be understood that any suitable driving means (not shown) may be provided for driving (rotating) the chain
120
, such as in the direction indicated by the arrow
126
.
The endless chain cutter
110
is elongate, having a top end
110
a
and a bottom end
110
b,
and having an overall length S which is greater than the desired resulting depth D of the trench
102
being excavated. For example, an endless chain cutter
110
having an overall length S of 30 meters may be disposed in a hole
108
which is only 20 meters deep. Typically, the underground portion of the endless chain cutter
110
is longer than the portion above the ground, so as to ensure stability and reduce the risk of the endless chain cutter
110
falling down.
The endless chain cutter
110
may be made up of several sections which are assembled together, in a known manner. For example, an endless chain cutter
110
having an overall length S of 30 meters may be made up of six sections—each section having a length of 5 meters. The endless chain cutter
110
is typically assembled in a vertical position, inside the hole
108
.
The endless chain cutter
110
is generally rectangular in cross section, having cross-sectional dimensions B and H. The cross-sectional dimension B is in the direction of the length L of the trench
102
being dug (excavated), and the cross-sectional dimension H corresponds to the resulting width W of the trench
102
. Typically, the dimension B is greater than the dimension H. For purposes of discussion, the chain
120
itself has a width (not labeled) which may be equal to the cross-sectional dimension H of the chain cutter
110
.
Evidently, as best viewed in
FIG. 1C
, the diameter of the hole
108
which is dug into the ground, into which the endless chain cutter
110
is disposed, corresponds to and should be slightly larger than the cross-sectional dimension B of the endless chain cutter
110
.
With the endless chain cutter
110
inserted into the hole
108
in the ground
104
, it is then moved along the X-axis, as indicated by the arrow
138
, to create the trench
102
having a length L. This is accomplished by mounting the endless chain cutter
110
in a suitable manner to a trolley
130
which preferably travels on two elongate rails
132
and
134
which are laid, parallel to one another, adjacent and parallel to the trench
102
desired to be dug.
The resulting trench
102
, and hence the resulting wall
160
being constructed in the trench
102
, is in the general form of a three-dimensional rectangular prism having a depth dimension D which is into the ground in the Z-axis, a length dimension L which is along the ground in the X-axis, and a width dimension W which is also along the ground in the Y-axis. The X-, Y- and Z-axes are mutually orthogonal to one another. As best viewed in
FIG. 1C
, the length L of the trench
102
is typically much larger than the cross-sectional dimension B of the endless chain cutter
110
. For example, the trench
102
and resulting wall
160
may be approximately 100 meters long and, as suggested above, approximately 20 meters deep. By way of further example, the width W of the trench
102
may be approximately 0.5-1.0 meters, the cross-sectional dimension H of the endless chain cutter
110
may similarly be approximately 0.5-1.0 meters, and
Fenwick & West LLP
Pezzuto Robert E.
SCC Technology, Inc.
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